In the case of a Thin Film Transistor (TFT) liquid crystal display device, the aperture ratio and the angle of visibility are important parameters for controlling the quality of the device.
A recently-developed In-Plane-Switching (IPS)-mode liquid crystal display device attracts a good deal of public attention as a liquid crystal display capable of realizing a very large angle of visibility. The IPS-mode liquid crystal display device generates an electric field in a direction horizontal to the array substrate by forming not only the display electrode but also the common electrode on the array substrate with the TFT formed on it and applying a voltage between the display electrode and the common electrode. Therefore, the liquid crystal material being present between the array substrate and the color filter substrate rotates in a plane while being kept horizontal to both the substrates. As the result, the IPS-mode liquid crystal display realizes an angle of visibility larger than that of the conventional Twisted Nematic (TN)-mode liquid crystal display device.
An IPS-mode liquid crystal display is superior in angle of visibility but it is inferior to the conventional TN-mode liquid crystal display in aperture ratio. A TN-mode liquid crystal display has a display electrode and a common electrode respectively constituted of a thin film made of transparent Indium Tin Oxide (ITO), while an IPS-mode liquid crystal display has a common electrode constituted of an ITO thin film and a display electrode made of a metal film of Aluminum (Al) or Molybdenum Tungsten (MoW). Because the display electrode made of the metallic thin film is opaque, the IPS-mode liquid crystal display has a low aperture ratio. As the aperture ratio lowers, the screen becomes darker. To improve the brightness of the screen, it is necessary to increase the number of backlights or the capacity of the backlight. And then, the liquid crystal display device is increased in size and weight and moreover, increased in power consumption. Therefore, the IPS-mode liquid crystal display having the superior characteristic such as a large angle of visibility is applied to a large liquid crystal display. However, application of the IPS-mode liquid crystal display to a notebook-type personal computer having many restrictions on power consumption, size, and weight has been suspended. Moreover, it can be considered that a large liquid crystal display lowers in the aperture ratio as the minuteness of the liquid crystal display is further improved and it is difficult to apply the IPS-mode liquid crystal display to the large liquid crystal display.
The TN-mode liquid crystal display has a large aperture ratio compared to the IPS-mode liquid crystal display. However, it is needless to say that it is preferable to obtain higher brightness at the same aperture ratio in order to improve the display characteristic and decrease power consumption.
Japanese Published Examined Patent Application No. 60-34095 and Japanese Published Unexamined Patent Application No. 63-121823 respectively disclose a liquid crystal display panel in which a polarization layer is set between two glass substrates. However, neither of them disclose any configuration for improving the light-recycling efficiency.
Therefore, it is an object of the present invention to provide a liquid crystal display panel and a liquid crystal display device capable of improving brightness without depending on the aperture ratio.